The prevalence of PTSD is estimated to be 7% in the general population, with approximately 24% of all individuals exposed to a significant trauma developing the disorder (Kessler et al., 1995). Relative to other symptoms of PTSD, symptoms of emotional numbing (i.e., loss of interest, interpersonal detachment, flattened affect) have demonstrated robust associations with reduced quality of life, social impairment, and poor treatment response. Despite the apparent impact of these symptoms, emotional numbing remains one of the least understood features of PTSD. Some theoretical models conceptualize numbing as an avoidance mechanism intended to dull the experience of emotions associated with the traumatic event. In support of this conceptualization, research has documented that individuals with PTSD may purposefully withhold expression of emotion. Basic research on emotion regulation indicates that withholding may result in attenuated positive affect, increased physiological arousal, and impaired social interaction;however, no study to date has examined the effects of manipulated expression within a trauma-relevant context. As such, it is hypothesized that expressive withholding may be a process that contributes to posttraumatic numbing. To explicate the impact of expressive withholding following exposure to a stressful event, the proposed research will utilize a film paradigm adapted from Gross and Levenson (1993;1997). Male and female participants will be asked to view three successive films - a neutral film (baseline), an analogue trauma film depicting graphic scenes of an actual suicide, and one of two experimental films containing a positively or negatively valenced scene. Prior to viewing the assigned experimental film, participants will receive instructions either to withhold expressive emotion during the film or just to watch the film segment carefully. Subjective affect and physiological activation will be recorded in response to each film. The specific aims of the proposed study are to 1) determine the effect of expressive withholding on the experience of discrete emotional states (i.e., amusement, sadness), 2) examine the impact of withholding on indices of higher- order emotion (i.e., valence, arousal) and 3) examine the effect of withholding on indices of sympathetic (i.e., skin conductance level) and parasympathetic (i.e., respiratory sinus arrhythmia) activation. PUBLIC HEALTH RELEVANCE: Emotional expression is believed to serve an important role for adaptive psychological, physiological, and social functioning. Research examining the impact of expressive withholding following trauma exposure may elucidate one potential mechanism contributing to posttraumatic numbing. Research in this area may assist in the development of techniques to augment existing treatments for PTSD